1. Field of the Invention
The present invention relates to a non-directional frequency generator, and more particularly to a non-directional frequency generator for converting direct current into alternating current.
2. Description of the Related Art
Generally, a non-directional frequency generator is a device for converting direct current into alternating current using a general relay or a semiconductor element, and a method that uses the semiconductor element such as a thyrister, etc., is mostly employed.
In such a semiconductor non-directional frequency generator circuit, a trigger circuit section is connected with a direct current power source, and a plurality of thyristers are alternately turned on/off by a switching operation of the trigger circuit section, and accordingly, the electric current flowing through a transformer reverses its direction. Accordingly, alternating current of a certain voltage is generated at an output end of the transformer.
In a conventional semiconductor non-directional frequency generator circuit, in order to generate a high output of alternating current, an expensive semiconductor element has to be employed, increasing the manufacturing cost. Further, there is a great loss of output of the semiconductor element due to the switching operation, while excessive heat is generated due to the output loss.
In order to solve the above-mentioned problems, a nondirectional frequency generator for converting the direct current into alternating current by using rotatable direct current inverting means was disclosed by the same applicant of this application in the Korean Patent Application No. 98-18589 (filed May 22, 1998), and the Korean Patent Application No. 98-21117 (filed Jun. 8, 1998), which are not published now.
Hereinafter, the above non-directional frequency generator will be briefly described with reference to the accompanied drawing as a related art.
FIG. 1 is a schematic view of a non-directional frequency generator driven by the direct current power source according to the related art.
Referring to FIG. 1, the non-directional frequency generator 100 includes a motor 110 driven by the direct current power source for generating a rotational force, a commutator 130 rotated by the motor 110, and a plurality of brushes in contact with an outer circumference of the commutator 130, such as the first, second, third, and fourth brushes 121-124 as shown in FIG. 1. The commutator 130 includes a cylindrical body 131, a conductive part which is divided into an even number of parts but divided into at least two conductive parts 132a and 132b on the circumferential surface of the body 131 as shown in FIG. 1, and an insulating part 133 formed therebetween on the circumference of the commutator body. Each of conductive parts 132a and 132b and at least two neighboring brushes of the first, second, third, and fourth brushes 121-124 are in simultaneous contact with each other. The direct current power source is connected with the first and third brushes 121 and 123, while the second and fourth brushes 122 and 124 are connected with a transformer T. First and second relays RY1 and RY2 turn on/off the operation of the non-directional frequency generator.
The operation of the non-directional frequency generator 100 will be described below: First, the first and second relays RY1 and RY2 are in on-state, and the commutator 130 is rotated by the motor 110. Accordingly, the brushes 121-124 in contact with the commutator 130 come into contact with the conductive part 132a, the insulating part 133, the conductive part 132b, and the insulating part 133 in a sequential manner, respectively.
More specifically, as the first brush 121 comes into contact with the conductive part 132a of the commutator 130, electric current flows through the positive terminal of the direct current power source DC, the first brush 121, the conductive part 132a of the commutator 130, the second brush 122, and then to the upper portion of a primary coil 202 of the transformer T downwardly to the low portion thereof. Then, the electric current flows through the second brush 122, the negative terminal of the direct current source DC via the conductive part 132b, and the third brush 123.
Next, while the commutator 130 is rotated, as the first brush 121 comes into the contact with the insulating part 133, the electric current does not flow through the commutator 130.
Then, as the commutator 130 rotates to ninety degree (90.degree.), the electric current from the positive terminal of the direct current source DC flows through the first brush 121 , and the conductive part 132b of the commutator 130, and the second brush 122, and reverses its direction upwardly to the upper portion of the primary coil 202 of the transformer T from the lower portion of the primary coil 202 of the transformer T. Then, the electric current flows through the fourth brush 124, the negative terminal of the direct current power source DC via the conductive part 132a of the commutator 130 and the third brush 123.
Accordingly, by the constant rotation of the commutator 130 of the non-directional frequency generator, the alternating current is generated at the primary coil 202 of the transformer T.
During the rotation of the commutator 130, each of brushes 121-124 comes in contact with the conductive part 132a, the insulating part 133, the conductive part 132b, and the insulating part 133 formed on the outer circumference of the commutator 130, in a sequential manner, respectively.
Meanwhile, different substances of the conductive parts 132a and 132b and the insulating part 131 of the commutator 130 cause various problems. That is, since heat is generated during the rotation of the commutator 130, the conductive parts 132a and 132b having high heat conductivity are heat-expanded and the expanded conductive parts 132a and 132b form coating layer on the insulating part 133. To prevent this phenomena, grooves 134 are formed between the conductive parts 132a and 132b and the insulating part 133.
However, since the grooves 134 are formed in perpendicular relation with respect to the rotating surface of the commutator 130, there is another problem of friction noise caused due to the collision of the edges of the grooves 134 with the brushes 121-124 during the rotation of the commutator 130.